1. Field of the Invention
The invention relates to a centrifugal fan having an upside-down mounted structure, and more particularly to a centrifugal fan having an upside-down mounted structure so as to possess a relatively long service life.
2. Description of the Related Art
Recently, electrical products tend to be smaller and thinner than ever. Notebook computers as described below for example, are getting thinner and thinner. A heat-dissipating device for a notebook computer includes a fan and a heat-dissipating plate for dissipating the heat energy generated during the computer operation. Therefore, the development of a relatively thin heat-dissipating device is in demand for a relatively thin notebook computer.
FIG. 4A is a top view of a conventional heat-dissipating device, and FIG. 4B is a front view of FIG. 4A. Referring to FIG. 4A, the heat-dissipating device includes an axial-flow fan 100 and a heat-dissipating plate 200. The axial-flow fan 100 includes a motor (not shown), a frame 101, and an axial-flow type of impeller 104. The motor used for driving purpose has a printed circuit board (not shown) positioned at its bottom, and the frame has four ribs 102 and an outlet 103 while the axial-flow impeller 104 has a hub 105 and a plurality of blades 106. In addition, a plurality of fins 201 and passages 202 are formed on the heat-dissipating plate 200 for dissipating heat.
Because the heat-dissipating device must be made relatively thin, the prior art in which the axial-flow fan 100 is directly mounted above the fins 201 cannot be adopted in a notebook computer or other similar electric products due to the limited thickness.
Referring to FIG. 4B, the heat-dissipating plate 200 is in L-shape and the axial-flow fan 100 is mounted on the right side surface of the heat-dissipating plate 200. When the axial-flow fan 100 rotates, the air is sucked in on one side and blown out on the other side, and the arrowheads indicate the direction of airflow. That is, the air flows from the topside of the axial-flow fan 100 into the axial-flow fan 100, and then, it flows from the frame 101 to the passages 202 of the heat-dissipating plate 200 to achieve the function of heat-dissipation.
The axial-flow fan of the prior art cannot provide relatively high air pressure either. The heat dissipating effect is relatively poor due to the interference of the plurality of fins 201. In addition, it is also due to the fact that the printed circuit board at the bottom of the motor is positioned close to the heat-dissipating plate 200 or even in direct contact with the heat-dissipating plate 200. In general, the temperature of the heat-dissipating plate 200 is much higher than that of the fan in operation. In this case, the relatively high temperature of the heat-dissipating plate 200 will shorten the service life of the fan.
FIG. 5A is a top view of a conventional heat-dissipating device, and FIG. 5B is a front view of FIG. 5A. Referring now to FIG. 5A, the heat-dissipating device includes an axial-flow fan without frames, and a heat-dissipating plate 400. The axial-flow fan includes a motor (not shown), a base 301, and an axial-flow impeller 304. The motor has a printed circuit board (not shown) at its bottom while the axial-flow impeller 304 has a hub 305 and a plurality of blades 306. The heat-dissipating plate 400 includes a plurality of fins 401, a fan seat 403, and an outlet 404. The plurality of fins 401 are used for dissipating heat, and the fan seat 403 is for receiving the axial-flow fan and providing flow ducts of the frameless type. And the outlet 404 is formed on the side surface of the fan seat 403 for the air to flow into the passage 402.
Referring to FIG. 5B, the axial-flow fan 300 is mounted inside the fan seat 403 of the heat-dissipating plate 400. The axial-flow fan 300 sucks the air into the fan seat 403 and discharges the air therefrom. The arrowheads indicate the direction of the airflow. That is, the air flows into the axial fan from the topside thereof, it then flows through the passage 402 of the heat-dissipating plate 400 and the outlet 404 to achieve the function of heat-dissipating.
The axial-flow fan of the above-mentioned prior art cannot provide a relatively high air pressure either. This is because that under the blocking effect of the plurality of fins 401, a relatively good radiation effect cannot be obtained.
In addition, the printed circuit board located under the motor is positioned close to or in direct contact with the heat-dissipating plate 400. In general, the temperature of the heat-dissipating plate 400 is higher than the temperature of the fan in operation. Therefore, the high temperature of the heat-dissipating plate 400 may shorten the service life of the fan. Furthermore, the heat-dissipating plate 400 of axial-flow fan applicable for using the frame-less type can not control the airflow produced by the axial-flow fan without the fan seat 403. The fan seat 403, the fins 401, and the passages 402 are integrally formed, and all of them are generally made of aluminum material. In case that the fan seat 403 is integrally formed with the axial-flow fan300, it is preferable that both the fan seat 403 and the axial-flow fan300 are made of plastic material that has a lower density than that of the aluminum material. Therefore, in comparison with the heat-dissipating device as shown in FIG. 4A, the weight of the heat-dissipating device as shown in FIG. 5A is increased further.
It is therefore one of the object of the invention to provide a centrifugal fan having an upside-down mounted structure capable of preventing the electric elements of the fan from being affected by the heat-dissipating plate with relatively high temperature in order to increase its service life. In addition, the centrifugal fan can also provide a better radiation effect than that of the conventional axial-flow fan.
In accordance with one embodiment of the invention, a centrifugal fan having an upside-down mounted structure is mounted on a heat-dissipating plate. The centrifugal fan includes a frame fixed on the heat dissipating plate and a stator upside-down mounted in the frame and fixed on the upper surface. The frame includes an upper surface positioned away from the heat-dissipating plate, a side surface substantially perpendicular to the upper surface, at least one inlet formed on the upper surface, and an outlet formed on the side surface. The stator includes a printed circuit board positioned close to the upper surface and positioned away from the heat-dissipating plate.
The frame may further includes a bearing seat connected to the upper surface of the frame and at least one rib formed on the upper surface of the frame for fixing the bearing seat. The at least one inlet is defined by the upper surface of the frame and the at least one rib.
It is preferable that the centrifugal fan having an upside-down mounted structure further includes a centrifugal impeller enclosing the stator and capable of rotating with respect to the stator. The centrifugal impeller includes a hub and a plurality of blades connected to the hub to form a plurality of connection portions positioned close to the heat-dissipating plate and positioned away from the upper surface of the frame.